1. Field
Aspects of embodiments of the present application relate generally to a method for controlling a motor and a system for controlling a motor.
2. Description of the Related Art
Hybrid systems for vehicles are already known (see, for example, Japanese Laid Open Patent No. 2001-339804). The hybrid system may have a motor (such as an electric motor) as a driving source in addition to an engine (such as a gasoline engine), wherein the motor (using, for example, electrical energy) may assist rotation of a crankshaft when the crankshaft rotates in a low rotation speed range as fuel is supplied to the engine. Though it is a tendency that the engine has a low torque in the low rotation speed range, the motor may generate a high torque in the low rotation speed range. Therefore, the motor may efficiently assist rotation of the crankshaft when the crankshaft rotates in the low rotation range.
In the hybrid system, the motor is operated as a generator to recover regenerative power from the motor when the crankshaft decelerates. In the hybrid system, when the vehicle stops, an idling stop is made and, thereafter, the engine is started again by using the motor. However, the motor used in a related art hybrid system has a problem in that the motor has back electromotive force that becomes very high as a rotation speed of a rotor increases. Therefore, if an inverter that connects the motor to a battery is not activated, the back electromotive force generated at the motor may act on the battery. In addition, if the voltage in the battery is low, the back electromotive force generated at the motor may cause battery faults.
Accordingly, in order to prevent the back electromotive force from causing battery faults, some of the hybrid systems (for example, a strong hybrid system, in which acceleration of the vehicle is possible only with the motor, or a mild hybrid system, in which the motor is used as an assist to the engine) make the voltage in the battery high for preventing battery faults from happening because of the back electromotive force. In such hybrid systems, the motor may be operated up to a high rotation speed range because of the high voltage in the battery. That is, these hybrid systems may drive the motor (such as a rotor within the motor) to be synchronized to the rotation of the crankshaft even in the high rotation speed range. However, such hybrid systems have problems in that the battery becomes large, expensive, and difficult to handle.
Consequently, in order to solve these problems, instead of using a strong hybrid system or a mild hybrid system, a micro-hybrid system is suggested. In a micro-hybrid system, the motor is driven by using a low voltage battery (for example, a battery having a voltage in a range of 30 V (volts) to 60 V). However, since the voltage in the battery is low, the micro-hybrid system may, for example, have to use a motor having an output lower than the strong hybrid system.
For instance, though the strong hybrid system may have a highest motor power of 60 kW (kilowatts), the micro-hybrid system may have a highest motor power of, for example, 1.8 kW (or about 1.8 kW). Moreover, the micro-hybrid system may use the motor for limited purposes, such as engine starting (including re-starting the engine after an idling stop), and recovery of the regenerative power from deceleration of the crankshaft in a medium rotation speed range or a high rotation speed range.
That is, in order to prevent battery faults caused by the back electromotive force, in the micro-hybrid system, the motor may not be capable of assisting the rotation of the crankshaft when the crankshaft rotates in a high rotation speed range. In other words, in the related art micro-hybrid systems, the motor may not be synchronized to the rotation of the crankshaft when the crankshaft rotates in a high rotation speed range. Moreover, in the micro-hybrid system, since the motor has a low output (e.g., a low torque), the motor also cannot assist the rotation of the crankshaft when the crankshaft rotates in a low rotation speed range.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present invention. Therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.